This invention relates to a method for processing a single-crystal semiconductor wafer, and more particularly to a method for processing a single-crystal semiconductor wafer for a fluorescent display device in semiconductor techniques, display techniques and the like.
Processing of a monocrystalline or single-crystal semiconductor wafer which has been conventionally carried out typically utilizes cutting by a dicing saw or formation of a line-like or stripe-like notches by a diamond cutter or cemented carbide blade cutter.
Breaking or cutting of a single-crystal semiconductor wafer by a dicing saw is carried out by means of cutting water. Such cutting water exhibits three functions or cooling characteristics of preventing an increasing in temperature of a cutting blade of the dicing saw due to frictional heat, cleaning characteristics of washing off swarf or cuttings produced during the cutting, and lubricating characteristics of reducing wearing of the blade during the cutting.
The above-described three functions are essential to cutting of a single-crystal semiconductor wafer by the dicing saw. In particular, in order to permit the cutting water to exhibit cleaning characteristics of removing swarf produced by the cutting, it is required to jet cutting water toward the blade.
However, a phosphor of a fluorescent display device is made of a water-soluble photosensitive material, resulting in failing to exhibit water-resistance. Thus, when cutting water is sprayed on the single-crystal semiconductor wafer under a pressure increased to a degree, it causes the phosphor coated on a picture cell on the single-crystal semiconductor wafer to be peeled from the semiconductor wafer.
Thus, in the prior art, cutting of the single-crystal semiconductor wafer has been carried out in any one of the following ways.
More specifically, a first way is that when the dicing saw is used, a dead space for a cut line of 2 mm or more is defined so as to prevent dissolution of the water-soluble photosensitive material due to spreading of cutting water around the cutting blade of the dicing saw during cutting of the wafer by the dicing saw from affecting the phosphor for the picture cell.
A second way is that line-like or stripe-like notches is formed on the single-crystal semiconductor wafer by means of a diamond cutter or a cemented carbide blade cutter, followed by breakage of the wafer in such a manner as seen in breakage of glass.
A third way is that half-cutting is carried out on the single-crystal semiconductor wafer by dicing prior to coating of the phosphor thereon and then the wafer is broken after the coating.
A fourth way is that after chips formed on the single-crystal semiconductor wafer are cut, the chips are coated thereon with a phosphor one by one.
The first way described above causes swarf to be left on a region of the single-crystal semiconductor wafer in proximity to a cut line when a reduction in amount of cutting water deteriorates cleaning characteristics of the cutting water. Also, putting of the swarf on the phosphor causes a reduction of luminance of the fluorescent display device and short-circuiting between element lines. Further, the first way requires to increase a width of the dead space for the cut line to a level as large as 2 mm or more so that scattering of the photosensitive material due to an increase in amount of cutting water to a degree sufficient to lead to dissolution of the water-soluble photosensitive material in the cutting water is kept from affecting the phosphor picture cell.
The second way causes generation of chippings increased in size, to thereby require to increase the dead space for the cut line as compared with dicing.
The third way causes the phosphor to be left in a dicing groove, so that the fluorescent display device in which the single-crystal semiconductor wafer is incorporated causes leakage luminescence at the cut line.
The fourth way, when slurry techniques are utilized therein, causes swelling of the phosphor on an edge of the chip, to thereby require separation between the edge of the chip and an element section of the chip. Unfortunately, this needs to increase the dead space to a dimension as large as about 10 mm.
Thus, in the fluorescent display device, the number of elements per one single-crystal semiconductor wafer is substantially varied depending on the dead space and an increase in dead space causes a reduction in number of elements per one wafer. Also, leakage luminescence as seen in the third way renders the fluorescent display device defective.